Apparatus for pumping fluids

ABSTRACT

This disclosure relates to a fluid pump for pumping fluids with opposed reciprocating pistons which periodically displace fluid between inlet and outlet ports. The pistons, which are mounted in a passage communicating with the ports, may be moved apart to provide an opening for accepting fluid from the inlet port. The pistons are next moved to a location adjacent the outlet port while the volume of the opening remains constant. The pistons are then moved together to close the opening and force the fluid through the outlet port. The volume of fluid displaced may be selectively varied.

United States Patent 1 3,695,788 Loomans [4 1 Oct. 3, 1972 APPARATUS FOR PUNIPING FLUIDS Primary Examiner-Ca.rlton R. Croyle [72] Inventor: Bernard A. Loomans, 3403 Weiss Assistant Examiner-Richard c'fick St., Saginaw, Mich. 48602 Attorney-barman & Mcculloch [21] Appl' 1707 This disclosure relates to a fluid pump for pumping fluids with opposed reciprocating pistons which [52] U.S.Cl ..417/488 periodically displace fluid between inlet and outlet [51] Int. Cl. ..F04b 37/00, F04b 19/00 ports. The pistons, which are mounted in a passage Field of Search communicating with the ports, may be moved apart to 92/205 provide an opening for accepting fluid from the inlet port. The pistons are next moved to a location ad- [56] References C'ted jacent the outlet port while the volume of the opening P remains constant. The pistons are then moved together to close the opening and force the fluid 1,568,269 1/1926 Cormier ..92/206 through the outlet port The volume f fl id displaced 3,464,359 9/1969 King et a]. ..417/488 may be Selectively varied 3,302,578 2/1967 Anderson ..417/488 11 Claims, 12 Drawing Figures RI R R2 P C 40b 4| 4o 40 H I29. f

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FIG IO INVENTOR. Bernard A Loo/270975 APPARATUS FOR PUMPING FLUIDS This invention relates to a positive displacement pump having a high volumetric metering accuracy. Liquid pumps of this type are required as volumetric liquid metering devices, for instance, in the chemical industry. The major advantage which metering pumps of the genera type disclosed herein have over other types of positive displacement pumps, such as geartype pumps, is their capability of producing high discharge pressures without erratic volumetric displacement. This is mainly due to the elimination of leakage. When check valves are utilized in a pump, serious difficulties arise when the liquid is either contaminated and carries solid particles in suspension, or when liquids with a high viscosity are being pumped. If solid particles, which can be in a form ranging from small crystalline particles through fiber-like particles to larger soft gels, are suspended in the liquid, they can become trapped between the valve and the valve seat, thus preventing the valve from closing. As soon as this happens the volumetric displacement of the pump becomes erratic, and eventually fluid displacement may stop altogether. If high viscosity liquids are being pumped, a similar situation can arise because the valves are surrounded by the liquid and their motion in the viscous liquid becomes too sluggish to follow the timing of the plunger stroke. As a result, the valves never fully open or fully close, with resulting unreliability and metering inaccuracies.

It is, therefore, a prime object of the present invention to provide a simple and reliable pump for pumping viscous liquids or low viscosity liquids carrying solid or semi-solid particles in suspension and achieving high discharge pressures.

It is a further object of this invention to provide a pump for pumping liquids which is selectively capable of varying the amount of liquid displaced per unit of time while the pump is in operation.

According to the present invention, there is provided a fluid pump, including inlet and outlet means, reciprocating means for displacing fluid between the inlet and outlet means, and control means for controlling the movement of the reciprocating means.

Other features of the invention will be apparent from a review of the following specification describing a preferred form of apparatus and reference to the drawing, in which:

FIG. 1 is a fragmentary view, partly in section, of the complete assembly of the pump according to a preferred embodiment of the invention;

FIG. 2 is an enlarged fragmentary side elevational view, partly in section, illustrating the details of the pump cylinder and plungers;

FIG. 3 is an eniarged, perspective elevational view of the control portion of the pump;

FIGS. 4A4l-I are diagrammatic illustrations illustrating the movement of the two plungers in the cylinder, which produce the pumping action;

FIG. 5 is a fragmentary schematic elevational view of the mechanism producing the plunger motion;

FIG. 6 is a fragmentary elevational view illustrating a slightly modified form of this mechanism;

FIG. 7 is a front elevational view of the cam which forms a part of the mechanism particularly shown in FIGS. 3 and 6;

FIG. 8 is a side elevational view of the cam taken along the line 8 8 of FIG. 7;

FIG. 9 is a front elevational view, partly in section, disclosing another embodiment of the invention;

FIG. 10 is a sectional view taken along the line 10 10 of FIG. 9;

FIG. 11 is a sectional view showing a piston seal mounted on the fluid displacement pistons utilized in the various embodiments of the invention; and

FIG. 12 is a cross-sectional view of the piston and seal taken along the line 14 14 of FIG. 11.

Referring now to the drawings, and particularly to FIGS. 1 3 thereof, a housing or frame F supports a fluid pump assembly generally designated P and having a reciprocating mechanism, shown generally at R, and a control mechanism shown generally at C for controlling the reciprocating mechanism. The inlet pipe 10 for the pump is connected between a suitable source of pressurized fluid, not shown, and! inlet port 10a communicating with cylinder 14a formed in pump housing 14. The outlet pipe 12 for the pump is connected with outlet port 12a of cylinder 14a. The pump housing 14 is connected to the housing F through the bracket 20.

The reciprocating mechanism R includes first and second, oppositely disposed portions designated generally R and R which are axially movable with respect to each other as will be explained more fully hereinafter. The reciprocating portion R includes a left end plunger 21 connected with a hollow cylindrical tube 22 by means of tie rods 23 connected with spaced apart yokes 24. The reciprocating portion R includes a right-end plunger 25 fixed directly to an axially extending bar 26 by any suitable means such as a key or a threaded connection (not shown). Plunger 21 moves with tube 22 and plunger 25 moves with the bar 26 which is slidably engaged with tube 22.

Cylinder chamber 14a communicates with the ports 10a and 12a and is adapted to receive the plungers 21 and 25. A pair of seals 28 and 29 are provided for opposite ends of the cylinder bore 14a to prevent the fluid which is being pumped from leaking. A cavity or opening 30 is formed between the ends of plungers 21 and 25 to receive fluid from inlet port 10a and transfer it to outlet port 12a, whence the plungers 21 and 25 close to reduce the cavity as will later appear. The plunger seals 32 and 34, shown particularly in FIG. 13 and to be described more fully hereinafter, prevent the fluid from flowing to or from cavity 30, except at ports 10a and 12a.

The operation of plunges 21 and 25 inside the cylinder 14 during one cycle will now be described with reference to FIGS. 4A 4H where their operation is depicted schematically. The position of the parts at the beginning the the pumping cycle is illustrated, shown in FIG. 4A, at which time the plunger ends 21a and 25a are spaced apart a distance X inside the cylindrical bore 14a (having a diameter D), thus creating an opening 30 having a volume equaling %1'rD X. In this position, both plungers are located such that the opening 30 between the plunger ends 21 and 25 is in open communication with the port 10a. During the time interval between FIGS. 4-A and 4-B, which represents 7i; of the total pumping cycle or 45 of rotation of the crankshaft 44 (FIG. 1), as will be described more fully hereinafter, the distance between the plungers 21 and 25 is increased to Y. During the time interval between FIGS. 4-B and 4C, again representing Vi; of the pumping cycle, the spacing 30 between the plunger ends is further increased to Z and the volume of opening 30 is increased to law-D 2. The opening 30 is, of course, filled with the fluid which is fed through port 10a under pressure. During the time interval from FIGS. 4C through 4D and to 4E, representing a total of M; of the pump cycle, the spacing 30 remains unchanged while both plungers travel together to the right. In position 4E, both plungers are located such that the volume of the space 30 between the plunger ends 37 and 32 is in open communication with the outlet port 12a. During the time interval from FIG. 4E to FIG. 4F, the spacing 30 is reduced from Z to Y. During the time interval from FIG. 4F to 4G, the spacing between the plunger ends 37 and 32 is further reduced to X, forcing the fluid through outlet port 12a. During the time interval from FIG. 46 through FIG. 4H to a position identical to FIG. 4A, the spacing 30 remains unchanged, while at the same time both plungers travel to the left to begin a new cycle.

It is plain from this description that during one pumping cycle a volume equal to Ari-D (X X) is transferred from the port 10a to the port 12a. It is further clear that in pumping non-compressible fluids, the spacing between the plunger ends must remain completely unchanged during the periods that the volume of fluid being transferred is not in open communication with either port 10a or port 12a because such a change would lead to extremely high stresses in the mechanism and unavoidable failure. Further, is is advantageous if the relative displacement between the two plunger ends 21a and 25a can be varied such that the volume transferred is selectively variable, preferably without stopping the pump. Mechanisms having the capability of fulfilling all these conditions will be described hereinafter.

The drive mechanism producing the plunger motion described in FIG. 4A 4H requires a combination of two independent motions. The first of these is an oscillating motion with a constant stroke, which moves both plungers with equal velocity from the inlet 10a to the discharge port 12a. During this basic motion a second relative motion is provided which produces the relative motions of two plungers at each end of the stroke to increase the space between the plungers at the inlet port and decrease this space at the discharge port. The second motion in the mechanism of the present invention is also selectively variable in magnitude.

Referring now to FIGS. 1 and 3, the control mechanism for producing these two motions is generally shown at C mounted in the housing F. Reference will be made to FIG. in first describing the control mechanism C, particularly shown in FIGS. 1 and 3, which controls the relative motion of the plungers 21 and 25 relative to the inlet and outlet ports a and 12a. A crankpin 36, connected to a shaft 44 by cam 45 and driven by a source of power such as a synchronous electric motor (not shown), rotates in a circle having a radius r. A connecting rod 37 connects the crankpin 36 to a lug 38 which is rigidly attached to the hollow cylindrical tube 22. Tube 22 is supported in tubular slide bearing members 39 and 390 which are rigidly attached to the housing F to enable tube 22 to slide lengthwisely in these bearings. Inside the hollow tube 22, the solid cylindrical bar 26 is supported such that it can slide lengthwisely inside, and relative to the tube 22. Connecting rod 40 has one end connected to bar 26 by pin 40a and at its other end is connected to an equilaterally formed triangular plate 41 by a pin 40b. The triangular plate 41 is pivotally connected to the lug 42 by a pin 42a, lug 42 being rigidly attached to the tube 22.

As shown in FIG. 5, upon rotation of the crankpin 36, the complete assembly of tube 22, bar 26, and plungers 25 and 21 will receive a lengthwise motion with a stroke equal to 2r during each complete revolution of shaft 44. If a pin 42b attached to triangular plate 41 and connecting it to actuating linkage, to be described, is moved vertically in an arc around pin 42a a distance D, the pin 40b moves horizontally to the left the same distance D. Through the Connecting rod 40, the bar 26 is moved to the left essentially the same distance relative to the tube 22. The manner in which pin 42b is moved vertically will be presently treated.

The portion of control mechanism C shown in FIGS. 1 and 3 for moving the first and second opposed movable portions R and R relative to each other will now be described. A cam follower roller 46 is connected to one end of a lever 47 which is pivotally supported on the pin 48a. As will be described more fully hereinafter, pin 48a is supported on a longitudinally adjustable stand, such as that shown at 50 in FIG. 1. At its opposite end, the lever 47 is connected by the pin 48 to a link 49 which forms the bottom link of a double parallelogram linkage shown generally at P. The double parallelogram linkage P includes link 49 which is connected with two links 50 and 500 which are connected at their upper ends by a link 51. The two links 52 and 52a which are connected at their lower ends to link 51 are connected at their upper ends to the triangular plate 41, by the pins 42a and 42b. The pin 49a which pivotally connects the lever 49 with link 50b is supported on the lug 18b which is rigidly attached to the frame F. The action of the double parallelogram is such that, regardless of the position of pin 420, which slides horizontally along with the tube 22, the links 49 and 51 and a line passing through the axes of pins 42a and 42b are always parallel, therefore, when the pin 48 undergoes a vertically upward movement, the link 49 swings upwardly and the equilateral triangle 41 rotates about the pin 42a. Simultaneously, the pin 40b swings to the left and through the connecting rod 40 and pin 40a, the bar 26 moves to the left relative to the tube 22 over essentially the same distance as the pin 48 moved upward.

The stand 50, according to the preferred embodiment, shown in FIGS. 1 and 3, adjustably mounts the pivot pin 48a which is attached to a nut 64 movably mounted in housing 65. Opposite ends of screw 66 are journaled in bushings 66a and 66b formed in the screw housing 65 mounted on frame F. The threaded portion of screw 66 passes through a nut 64 which is adapted to reciprocably slide in a channel 65b formed in housing 65. By turning hand crank 67, screw 66 moves nut 64 and pin 48a to the right or left, as desired. By lengthwise movement of pivot 48a, the pump displacement can be varied through the variation of the relative movement of the plungers. It is thus clear that the more pin 48a, which is the pivot of lever 47, is moved to the left, the longer the lever arm between pin 48a and the roller 46 becomes, and the shorter the lever arm between the pin 48a and the pin 48 becomes. Thus, the vertical motion of the pin 48, and consequently the relative motion of the bar 26 with respect to the tube 22, is variable depending upon the position of the pin 48a.

As can best be seen in FIG. 3, the roller 52a is connected to the roller 46 by the link 70 and laterally guided by the link 71. The two rollers 117 and 46 cooperate through link 70 to maintain the rollers in engagement with the cam 45 at all times. If desired, the axis of the pivot pin 48a can be made to coincide with the axis of the pin 48 in FIG. 3. This results in a zero motion of the pin 48, and thus zero displacement of the pump. The importance of this mechanism is that the displacement of the pump can thus be varied from zero or a very small displacement to maximum displacement without stopping the mechanism. The cam 45, shown in FIGS. 1 and 3 will be described by referring to FIGS. 7 and 8, which show the symmetrically formed cam 45 in detail. The cam profile consists of two circular sectors, one with a radius r,, and one with a radius r connected by two portions c on either side. Both circular sectors have an arc length B substantially equal to 90. The crankpin 36, which is attached to the cam at a radius r from the shaft axis, is angularly off set by an angle A from the line of symmetry of the cam. The reason for this will become clear from the description of the operation of the mechanism.

When the shaft 44 rotates in the direction indicated by the arrow s, the tube 22 with its attachments is moved to the right by the crank pin 36 through the connecting rod 37. The cam follower roller 46 is at this time following the concentric circular section of the cam 45 having radius r (see FIG. 7). When the cam 45 has turned through an angle equal to of angle B, or approximately 45, the cam follower 46 contacts the noncircular curved part of the cam 45 and starts to move downward. Just before this downward movement, pistons 21 and 25 will be in the position shown in FIG. 4E. During the downward movement the lever 47 is rotated in a clockwise direction around the pivot 48a. This causes the pin 48 to swing upwardly, and through the double parallelogram also causes pin 42b to swing upwardly around the pivot 42a. This, in turn, through the pin 40b and the connecting rod 40, causes the bar 26 to move to the left relative to the tube 22. Thus, while the tube 22 slides to the right, the bar 26 moves inside and relative to the tube 22 to the left. This motion continues until the cam has rotated over the full nonconcentric curved part c, or approximately 90, and the cam follower roller 46 starts to contact the concentric circular sector of the cam with radius r,. This 90 of cam movement corresponds to the movement of pistons 21 and 25 from the position shown in FIG. 4E through FIG. 4F and to the positionshown in FIG. 4G. During this time the crank 36 rotates from position 53 to position 54 in FIG. 5. The roller 46 has thus swung down around the pivot 48 over a distance equal to r, r When pivot 48 is in the position shown in the drawing relative to lever 47, the length of the lever from the center of the roller 46 to the pivot 48a is equal to the lever length between 48 and 480. Hence, pin 48 moves up a distance equal to r r which is also the distance D moved by pin 42b.

Since the sides of the triangle formed by the pins 42b, 42a and 40b are equal, pin 40b and rod 40 also move a distance D and the rod 26 moves relative to and inside the tube 22 to the left over distance essentially equal to r r This 90 movement over the noncircular portion of the cam corresponds to movement of pistons 21 and 25 from the position shown in FIG. 45 through the position of FIG. 4F to that shown in FIG. 4G.

Over the next 90 rotation of the cam, the roller 46 follows the circular part with radius r,, which does not cause any vertical movement of the roller 46. Thus, the relative positions of the tube 22 and the bar 26 remain unchanged. During this period the crank 36 rotates from position 54 to position 55 in FIG. 5 and moves the tube 22 with its attachments to the left. This 90 circular movement corresponds to the movement of plungers 21 and 25 from the position shown in FIG. 4G to that shown in FIG. 4A. At this time, the roller 46 contacts the nonconcentric curved part of the cam between radius r and radius r and! consequently, while the crank 36 moves from position 55 to position 56, the roller 46 swings upward a distance r r and the bar 26 is moved over essentially the same distance to the right inside and relative to the tube 22. Here the cam movement corresponds to movement of pistons from the position shown in FIG. 4A to that shown in FIG. 4C. Further rotation of the crank about radius r returns the pistons to the position shown in FIG. 4E. It is thus obvious that at each end of the stroke of the crank 36 between positions 55 and 56, and between positions 53 and 54 in FIG. 5, the bar 26 undergoes a relative movement with respect to the tube 22. At the right hand end of the stroke the bar 26 is pushed out of the tube 22, and at the left hand end of the stroke it is pulled into the tube.

The embodiment illustrated in FIG. 6 is similar to that of FIG. 1, however, the rollers 117, and links and 71 have been replaced by a spring 115 urging the roller 46 of the slotted lever 47 into contact with cam 45. The lever 47' isslotted at 63 to receive the pivot pin 48a mounted on thestand 50' which is longitudinally, adjustably mounted on frame F by bolts 62 passing through an elongated slotted opening t in the base of frame F. Thus, if bolts 62 are loosened, the stand 50 can be slid to the left which allows the pin 48a to slide in the groove 63 over a distance L. The operation of this embodiment is similar to that of FIG. 1 and the description will not be repeated.

Referring now to the alternate embodiment shown in FIGS. 9 and 10 wherein the movable portions R, and R of the reciprocating means consist primarily of plungers 21 and 25 mounted in opposed relation in cylinder 14a, the housing F which is similar to housing F includes an opening 86' with a support member 75 spanning the opening. Member 75 forms a support for cylinder 14a and the bearings 39b and bearings 390 are formed in opposite sides of housing, F Plungers 21 and 25 are slidably mounted in bearings. 39b and 39c.

The two plungers 21 and 25 are connected to a pair of connecting rods 76 and 77 by pins 78 and 79, respectively. At their point of intersection, rods 76 and 77 are connected to block 80 by pins 810 extending from opposite sides of block 80. Block 80 is slidably mounted on a guide bar 81 (FIG. 10) which 81 is rigidly connected to a bar 82 which is slidable vertically in bearings 83 and 84. The pin 85 connects a lever 86 which pivots on a pin 87 to bar 82. At its other end, lever 86 is connected with a roller 88 which is connected to roller 89 by a link 90, such that this combination follows the contour of the cam 45 when it rotates. Roller 89 is connected with a lug 75a on support 75 by means of arm 89a and pin 89b. The crank pin 36 which is attached to the cam 45 is connected to the pins 81a by a connecting rod 91 which may conveniently comprise an extension of link 77. Upon rotation of the crank 36, pins 81a move horizontally back and forth with a stroke equal to the diameter of the crank circle. This would normally result in block 80 sliding to and fro on guide bar 81 and plungers 21 and 25 being moved relative to inlet and outlet ports 10a and 12a without being moved relative to each other. The move ment of plungers 21 and 25 relative to each other is dependent upon the vertical movement of pivot pins 81a. When the pins 810 move down vertically as a result of the downward motion of the guide bar 81, they pull the plungers 21 and 25 closer together through the scissors action of the connecting links 76 and 77. When pins 81a move upward, plungers 21 and 25 move apart.

The vertical movement of pins 81a is dependent upon the vertical movement of bar 80 and lever 86 which depends upon the position of cam 45. As the roller 88 moves up, pin 85 and bar 82 move downward, causing plungers 21 and 25 to move closer together. As roller 88 moves down, pin 85, bar 82, and pin 81a move upward, causing plungers 21 and 25 to move apart. The movement of plungers 21 and 25 relative to ports 10a and 12a is similar to that illustrated in FIGS. 4A 4H, and will not be repeated. The inlet and outlet ports are reversed in position in the view, as will be noted. The cam and crank combination which is driven by an outside power source not shown operates in such a manner that, at the right hand end of the crank stroke, the plungers are pushed apart when the cavity between them is in open communication with the inlet 10a. At the left hand end of the stroke they are brought close together when they are in communication with the discharge port 12a, thus creating a pumping action as described before.

Pivot pin 87 which is fixed to bracket 89 is slidably mounted in a slot 23a formed in lever 86. Bracket 89', which is slidably mounted in a slot S in the housing, has an internally threaded portion adapted to receive screw 92a which is journaled in the housing at 92b and 920. By turning hand crank 92d, screw 92a moves the bracket 89 and pin 87 to the right or left, as desired. Hence, the displacement of the pump can be varied by changing the limits of the movement of one plunger relative to the other.

Referring now to FIGS. 11 and 12 for a specific disclosure of the plunger mechanism, the plunger 21a is shown removed from its cylinder 14 and is shown connected to the driving mechanism R by the open coupling 108 which is located outside the cylinder 14 and comprises separate halves clamped together by the bolts 109. Coupling 108 allows access to the hexagon head 1 10 of a bolt 1 11, which has a cylindrical foot 1 12 fixed on its other end. A tapered nut 113 is in threaded engagement with the bolt 111, and supports a resilient seal 114 having a complementally tapering bore. The seal 114 which is preferably formed of a semi-hard neoprene or fluorocarbon, is subject to wear. When a seal 114 wears to a point where internal liquid leakage takes place, a slight turn of the hexagon head of bolt 111 will move the tapered nut 113 to the left to radially expand the seal 114 and reseal the plunger against leakage. A lock nut 110a may then be retightened to lock bolt 111 in position. The sealing pressure is adjustable in this way without requiring disassembly of the machine.

The invention is defined in the claims.

Iclaim:

1. Apparatus for pumping liquids comprising:

a frame;

a pump housing on said frame having an axial passage therein and inlet and outlet ports at inlet and outlet pumping stations communicating with said passage;

first and second pistons therein a common driving source;

first connecting means connected with said driving source and said first and second pistons for simultaneously moving said first and second pistons in a to-and-fro axial path of travel between said inlet and outlet stations while maintaining their relative axial positions; and

second connecting means always intercoupling said common driving source and only one of said pistons for moving the pistons relative to each other in timed relation with the composite movement of said pistons in said path of travel such that said one piston moves away from the other at said inlet station to receive liquid therebetween from said inlet port and toward said other at said outlet station to discharge the liquid through said outlet port.

2. The apparatus set forth in claim 1 wherein said first connecting means comprises a sub-frame mounted on said frame for axial movement relative thereto, and linkage means connected to said sub-frame and said driving source for moving said sub-frame in said toand-fro path of travel, said other piston being fixed to said sub-frame for movement therewith in said to-andfro path, said one pistons being supported on said subframe for movement therewith as said sub-frame moves in said to-and-fro path and for axial movement relative thereto at said inlet and said outlet stations, said second linkage means comprising additional linkage means connected to said driving source and said one piston for moving said one piston relative to said other piston and said sub-frame at said inlet and outlet stations.

3. The apparatus set forth in claim 1 wherein said common driving source comprises a rotary cam means, said first connecting means comprises first linkage means coupled to said cam means for translating rotary motion of said cam means into linear motion of said pistons, said second connecting means comprises second linkage means including cam follower means reactable with said cam means for effecting said relative movement.

4. The apparatus set forth in claim 1 wherein said pistons each include a surrounding seal having adjustable means connected thereto for urging said seal into sealing engagement with the housing adjacent said passage.

5. The apparatus set forth in claim 1 including means for selectively varying the volume of fluid displaced between said ports even while said pistons are moving between said inlet and outlet stations.

6. The apparatus set forth in claim 5 wherein said second linkage means comprises lever means swingably mounted about a fulcrum on said frame, means biasing one end of said lever into engagement with said cam means, the other end of said lever being connected to said one piston for moving it relative to the other piston when said cam means rotates and pivots said lever about said fulcrum.

7. The apparatus set forth in claim 6 wherein said means for selectively varying the volume comprises means for selectively adjusting the position of said fulcrum relative to the opposite ends of said lever to control the relative movement of said pistons.

8. The apparatus set forth in claim 6 wherein said biasing means comprises additional linkage means connected to said one end of said lever engaging said cam means and including a cam follower engageable with the opposite side of said cam means.

9. The apparatus set forth in claim 3 wherein said second linkage means includes drive means movable in a to-and-fro path of travel generally transverse to the axial path of travel of said pistons, and means reactable between said drive means and said pistons for forcing the pistons together when said drive means moves away from said pistons and for forcing the pistons apart when said drive means moves toward said pistons.

10. The apparatus set forth in claim 9 wherein said means for axially moving said pistons includes means slidably mounted on said drive means for movement in a to-and-fro axial path of travel.

1 1. Apparatus for pumping liquids comprising:

a frame;

a pump housing on said frame having an axial passage therein and inlet and outlet ports in inlet and outlet pumping stations communicating with said passage;

a pair of opposed pistons disposed in said passage for axial movement;

a common piston driving source;

first connecting means connected with said driving source and said opposed pistons for simultaneously compositely moving said opposed pistons in a to-and-fro axial path of travel between said inlet and outlet stations while maintaining their relative axial positions;

second connecting means always intercoupling said common driving source and only one of said pistons for moving the pistons relative to each other in timed relation with the composite movement of said pistons in said path of travel such that said pistons move away from each other at said inlet station to receive liquid therebetween from said inlet port and toward each other at said outlet station to discharge the liquid through said outlet port; and

means connected with said first and second connecting means for selectively varying the volume of fluid displaced between said ports even while said pistons are moving between said inlet and outlet stations. 

1. Apparatus for pumping liquids comprising: a frame; a pump housing on said frame having an axial passage therein and inlet and outlet ports at inlet and outlet pumping stations communicating with said passage; first and second pistons therein a common driving source; first connecting means connected with said driving source and said first and second pistons for simultaneously moving said first and second pistons in a to-and-fro axial path of travel between said inlet and outlet stations while maintaining their relative axial positions; and second connecting means always intercoupling said common driving source and only one of said pistons for moving the pistons relative to each other in timed relation with the composite movement of said pistons in said path of travel such that said one piston moves away from the other at said inlet station to receive liquid therebetween from said inlet port and toward said other at said outlet station to discharge the liquid through said outlet port.
 2. The apparatus set forth in claim 1 wherein said first connecting means comprises a sub-frame mounted on said frame for axial movement relative thereto, and linkage means connected to said sub-frame and said driving source for moving said sub-frame in said to-and-fro path of travel, said other piston being fixed to said sub-fraMe for movement therewith in said to-and-fro path, said one pistons being supported on said sub-frame for movement therewith as said sub-frame moves in said to-and-fro path and for axial movement relative thereto at said inlet and said outlet stations, said second linkage means comprising additional linkage means connected to said driving source and said one piston for moving said one piston relative to said other piston and said sub-frame at said inlet and outlet stations.
 3. The apparatus set forth in claim 1 wherein said common driving source comprises a rotary cam means, said first connecting means comprises first linkage means coupled to said cam means for translating rotary motion of said cam means into linear motion of said pistons, said second connecting means comprises second linkage means including cam follower means reactable with said cam means for effecting said relative movement.
 4. The apparatus set forth in claim 1 wherein said pistons each include a surrounding seal having adjustable means connected thereto for urging said seal into sealing engagement with the housing adjacent said passage.
 5. The apparatus set forth in claim 1 including means for selectively varying the volume of fluid displaced between said ports even while said pistons are moving between said inlet and outlet stations.
 6. The apparatus set forth in claim 5 wherein said second linkage means comprises lever means swingably mounted about a fulcrum on said frame, means biasing one end of said lever into engagement with said cam means, the other end of said lever being connected to said one piston for moving it relative to the other piston when said cam means rotates and pivots said lever about said fulcrum.
 7. The apparatus set forth in claim 6 wherein said means for selectively varying the volume comprises means for selectively adjusting the position of said fulcrum relative to the opposite ends of said lever to control the relative movement of said pistons.
 8. The apparatus set forth in claim 6 wherein said biasing means comprises additional linkage means connected to said one end of said lever engaging said cam means and including a cam follower engageable with the opposite side of said cam means.
 9. The apparatus set forth in claim 3 wherein said second linkage means includes drive means movable in a to-and-fro path of travel generally transverse to the axial path of travel of said pistons, and means reactable between said drive means and said pistons for forcing the pistons together when said drive means moves away from said pistons and for forcing the pistons apart when said drive means moves toward said pistons.
 10. The apparatus set forth in claim 9 wherein said means for axially moving said pistons includes means slidably mounted on said drive means for movement in a to-and-fro axial path of travel.
 11. Apparatus for pumping liquids comprising: a frame; a pump housing on said frame having an axial passage therein and inlet and outlet ports in inlet and outlet pumping stations communicating with said passage; a pair of opposed pistons disposed in said passage for axial movement; a common piston driving source; first connecting means connected with said driving source and said opposed pistons for simultaneously compositely moving said opposed pistons in a to-and-fro axial path of travel between said inlet and outlet stations while maintaining their relative axial positions; second connecting means always intercoupling said common driving source and only one of said pistons for moving the pistons relative to each other in timed relation with the composite movement of said pistons in said path of travel such that said pistons move away from each other at said inlet station to receive liquid therebetween from said inlet port and toward each other at said outlet station to discharge the liquid through said outlet port; and means connected with said first and second connecting means for selectively varying the volume of fluid disPlaced between said ports even while said pistons are moving between said inlet and outlet stations. 